Illumination devices comprising a transmissive ceramic layer are known in the art. Transmissive ceramic layers or luminescent ceramics, and their method of preparation, are known in the art. It is for instance referred to US200510269582. US2005/0269582 amongst others describe a semiconductor light emitting device combined with a ceramic layer which is disposed in a path of light emitted by the light emitting layer. The ceramic layer is composed of or includes a wavelength converting material such as a luminescent material.
Illumination devices with a transmissive cover and a luminescent material are for instance described in US2007/0114562. This document describes for instance yellow and red illumination systems, including a semiconductor light emitter, and a luminescent material. The systems have an emission falling within the respective ITE red and yellow color bins having specified color coordinates on the CIE chromaticity diagram. The luminescent material may include one or more luminescent materials. The illumination systems may be used as the red and yellow lights of a traffic light or an automotive display.
US2007/0114562 further describes a LED illumination system comprising a support on which the semiconductor light emitter is disposed, a cover disposed on the support over the semiconductor light emitter, the cover and the support cooperatively defining an interior volume containing the semiconductor light emitter; and an encapsulant disposed in the interior volume and encapsulating the semiconductor light emitter. The luminescent material is deposited on an inside surface of the cover.